The present invention relates to a spherical granule of a water-soluble azo compound, and a process for producing the same.
As azo compounds which are highly useful as a radical polymerization initiator, etc. for producing high polymer compounds such as water absorbing resin, high polymer coagulant, etc., there have been known the compounds represented by the formulas (1) and (2). With the progress of a polymerization apparatus, e.g. scale enlargement, automating and energy-saving, azo compounds which cause no binding and agglomeration and have a shape suitable for charging smoothly at the time of introduction have been strongly requested. Further, since some water-soluble azo compounds have skin irritant action, products having a shape which causes no dust have been requested in view of safety.
However, there is a large risk and a fear of deterioration of quality in granulation by means of a normal granulation method because these compounds have high thermal decomposition properties and explosive properties. Therefore, a trial on granulation of these azo compounds have hardly been made, heretofore.
As the prior art in this field, there have been known a granulation method by means of an extrusion granulation publication is described in JP-A-99045/1988. This method directed to a method which comprises adding water to a powder, kneading the resulting mixture to adjust a binding power of the powder, and after compressing to minimize voids, extruding the kneaded mixture through a hole having a specific shape and then granulating the extrudate with a granulator, pelleter, etc. However, since the granules obtained by this method have a cylindrical shape, rolling fluidity is not sufficient. Therefore, abnormality such as choking sometimes arises in the introduction step. Further, the granules have a shape wherein corners are liable to be broken off and, therefore, generation of dust can not be sufficiently inhibited. Further JP-A-99045/1988 also describes a spray-granulation method and rolling-granulation method but these methods can not afford a spherical granule of the present invention.
An object of the present invention is to solve the above problem and to provide a spherical water-soluble azo compound wherein generation of dust is hardly arises, and a process for producing the same.
The above and other objects of the invention will become apparent from the following description.
The present invention provides a process for producing a spherical granule of a water-soluble azo compound, which comprises dispersing a water-soluble azo compound in a water-insoluble solvent and then adding dropwise water and/or a hydrophilic solvent which dissolves the water-soluble azo compound with stirring to granulate the water-soluble azo compound in the solution, and produce the spherical granule of the water-soluble azo compound.